According to Hindu calendar, the month of Shravan is dedicated to Lord Shiva. The entire month is considered highly auspicious to seek blessing of Lord Shiva. Devotees observe various fasts during Shravan month to appease Lord Shiva.
In North India, Shravan month is also known by the name Sawan month. All Mondays or Somwars in Shravan month are regarded as highly auspicious for fasting and they are known as Shravan Somwar or Sawan Somwar Vrats. There are several devotees who observe sixteen Mondays or Solah Somwar fasting from the first Somwar of Sawan month.
Tuesdays or Mangalwar in Shravan month are dedicated to Goddess Parvati. Fasting observed on Tuesdays in Shravan month is known as Mangal Gauri Vrat. Other auspicious days in Shravan month include Sawan Shivaratri and Hariyali Amavasya.
There is a difference of fifteen days in the starting time of Shravan month depending on the lunar calendar followed in the region. In the Purnimant calendar followed by North Indians, Shravan month starts fifteen days before the Amavasyant calendar.
Lunar Calendar is followed in Andhra Pradesh, Karnataka, Tamil Nadu, Goa, Maharashtra and Gujarat, Amavasyant. North Indian states Rajasthan, Uttar Pradesh, Madhya Pradesh, Punjab, Himachal Pradesh and Bihar follow Purnimant Calendar. This results in difference in dates of Sawan Somwar in both calendars.